iLife '11 compatibility with OS X 10.5.8

I have an iMac and a MacBook running on OS X 10.5.8 and a Mac Mini running 10.6.8. Is iLife '11 compatible with these three systems or do I have to upgrade all th eoperating systems first? I have been leery of OS upgrades as I fear losing things. I an running imeMachine on all three but have never had goo dexperiences with operating system upgrades back when I was in the PC world.